Amato, Paola (2025) Eco-sustainable design of hybrid redox-active materials for the removal of microplastics from water. [Tesi di dottorato]

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Abstract

Microplastics pollution has become one of the main environmental problems, and the issue of plastic wastes accumulation is a severe threat to whole ecosystem. This study is focused on the design and synthesis of hybrid materials, constituted by a semiconducting metal oxide (ZnO or TiO2) conjugated to a biowaste material (humic substances or rosin), that play an active role in the photodegradation of common widely used polymers, such as linear low-density polyethylene (LLDPE), polylactic acid (PLA) and polyethylene terephthalate (PET). Hybrid ZnO- and TiO2-humic substance nanoparticles were synthesized through solvothermal methods, and their ability in the photodegradation of LLDPE and PLA under UVA/solar illumination was explored. The development of innovative chemical approach for the treatment of microplastics, based on an oxidative process that does not require any direct energy source (irradiation or heat) is one of the main results of this research activity. It is based on a new hybrid TiO2-based material (T-Abi), that was synthesized through a simple sol-gel synthesis procedure, in which titanium is conjugated with a bio-waste, rosin, mainly constituted by abietic acid. The ligand-to-metal charge transfer complexes formed between rosin and Ti4+ allow the generation of reactive oxygen species without UV irradiation for its activation. In agreement with theorical calculations, superoxide radical ions are stabilized at ambient conditions on the surface of T-Abi allowing to obtain an impressive degradation of LLDPE after 1 month exposure in a batch configuration under indirect daylight illumination. Likewise, preliminary results concerning the chemical degradation of PET in the same conditions were also obtained. Furthermore, the chemical surface degradation of polytetrafluoroethylene (PTFE) magnetic stir bars was revealed for the first time, due to the effect produced by the oxidative activity of T-Abi under indirect daylight conditions. The innovative and sustainable approach developed in this PhD research activity represents a promising cost-effective strategy for the oxidative degradation of microplastics, without producing any toxic by-products. The findings unlock the potential of T-Abi in advancing environmental remediation and promoting a circular bioeconomy.

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